Search Results (239)

N-acetylornithine aminotransferase (AcOAT) is a pyridoxal 5′-phosphate (PLP)-dependent enzyme that catalyzes a key transamination step in arginine biosynthesis. In cyanobacteria, arginine metabolism is closely associated with nitrogen assimilation and storage, yet biochemical information on cyanobacterial AcOATs remains limited. In this study, the AcOAT encoded by the cce_3094 gene from Crocosphaera subtropica ATCC 51142 (CsAcOAT) was cloned, heterologously expressed, purified, and systematically characterized. Recombinant CsAcOAT was obtained as a soluble protein with an apparent molecular mass of approximately 43 kDa. Steady-state kinetic analysis showed that CsAcOAT catalyzed transamination between N-acetylornithine (AcOrn) and α-ketoglutarate (α-KG), with apparent K_M values of 0.17 ± 0.03 mM for AcOrn and 0.020 ± 0.003 mM for α-KG, indicating a higher affinity for α-KG. The enzyme exhibited optimal activity at pH 8.5 and 30 °C, retained relatively high activity over a broad temperature range of 0–50 °C, and was activated by Zn²⁺ and Co²⁺ but inhibited by Ni²⁺. Structural analysis based on homology modeling, molecular docking, and molecular dynamics simulations suggested a conserved PLP-dependent aminotransferase fold and a stable binding mode for the PLP-AcOrn complex in the active-site pocket. Site-directed mutagenesis further demonstrated that Gly114, Asp239, Lys268, and Thr296 are indispensable for catalytic activity, whereas Ser113, Ala115, and Gln242 make important contributions to catalytic turnover and cofactor-assisted catalysis. These results provide biochemical and structural characterization of CsAcOAT, expand current knowledge of cyanobacterial AcOATs, and offer a useful basis for future studies on arginine metabolism and nitrogen storage in diazotrophic cyanobacteria. Full article

Natural bentonite, dominated by montmorillonite-type layered aluminosilicates, is increasingly considered as an inexpensive and environmentally acceptable support or catalyst for the thermochemical conversion of waste carbon streams. Its relevance to catalysis arises from a combination of cation-exchange capacity, swelling behavior, hierarchical porosity after modification, and the possibility of generating Brønsted, Lewis, redox and metallic active sites. This review critically evaluates bentonite modification strategies—acid activation, alkaline and sodium exchange, inorganic oxide pillaring, transition- and noble-metal impregnation, organosilane or surfactant functionalization, and carbon-based hybridization—with emphasis on their consequences for texture, acidity, thermal stability, metal dispersion and catalytic behavior. The review then connects these structure–property relationships with the emerging application of modified bentonites in plastic-waste thermocatalysis and hydrogen-rich product formation. The recent literature indicates that acid-modified bentonite can substantially improve liquid hydrocarbon formation from polyethylene, binder-free bentonite pellets can operate at kilogram-batch scale for drop-in fuels, and Ni-, Fe- or Ni–Fe-modified bentonite-type catalysts can promote tar cracking, reforming and gas upgrading. However, direct evidence for high hydrogen yields from plastic waste over bentonite remains narrower than the evidence for liquid-fuel production, biomass pyrolysis or model-compound reforming. Therefore, this article distinguishes between direct plastic-waste evidence and transferable evidence from biomass, acetic acid, tar and hydrocarbon reforming studies. The analysis identifies Ni-impregnated acid-activated or pillared bentonite, Ni–Fe/bentonite, and La/Ca-promoted Ni/bentonite as the most promising routes for plastic-derived hydrogen-rich syngas, while acid activation alone is best regarded as a pretreatment rather than a complete catalyst design. Key limitations include catalyst deactivation by coke, metal sintering, chloride poisoning from PVC, inconsistent reporting of gas yields, and insufficient life-cycle and techno-economic analysis. A roadmap is proposed for designing reproducible, scalable bentonite catalysts for circular plastic-waste valorization. Full article

Understanding the mechanical behavior of bimetallic nanoparticles under compressive stress is relevant for the use of these nanostructures in catalysis and nanomechanics. In this work, we present molecular dynamics (MD) simulations of compressive deformation in Pt–Ni nanoparticles—and bulk systems for comparison—with varying compositions (Pt_xNi_1−x) and local distributions. The simulations show that the mechanical response is governed by local strain fields, which influence both elastic and plastic regimes. The final trajectories were analyzed by dislocation analysis (DXA), simulated STEM imaging, and geometric phase analysis (GPA), which allowed the obtention of high-resolution strain maps. Analysis of von Mises stress distribution allowed us to correlate composition and atomic ordering with the formation and evolution of dislocations in the nanoparticles. The Pt_0.5Ni_0.5 intermetallic compound exhibits superior mechanical performance under uniaxial compression; in bulk, this composition also shows enhanced elastic energy storage. In polycrystalline nanoparticles, energy dissipation increased with decreasing average grain size, which is attributed to elevated plastic activity induced by the presence of multiple crystallographic orientations. GPA results show that it is possible to discriminate between compositions differing by as little as $\mathrm{\Delta }x$ = 0.1 based on local strain distributions, and the comparison with GPA performed on real STEM micrographs gives a fair agreement. GPA and atomistic stress maps reveal how strain fields evolve during compression and how they correlate with the development of plasticity. These findings highlight the critical role of local structural heterogeneities in dictating the mechanical behavior of nanoscale Pt–Ni systems, and provide strong evidence that GPA can correlate local strain and composition in real high-resolution micrographs. Full article

The activity and stability of Ni-based catalysts for CO₂ methanation strongly depend on the morphology and chemical composition of the support. In this work, Ni catalysts with four oxidic supports (SiO₂, Al₂O₃, CeO₂, ZrO₂) were synthesized via a one-step spray pyrolysis approach. Comprehensive characterization by STEM-EDS, XRD, and N₂ adsorption was used to resolve support morphology, Ni particle size, and nanoparticle incorporation into the support matrix. Beyond steady-state activity and reaction mechanism, the support material also affects the activation period and initial stability of the catalysts. By combining temperature-programmed methanation scans on fresh and spent samples with long-term stability tests, we clearly identify support-dependent changes in initial activity and their correlation with Ni–support interactions. Enhanced physical embedding and stronger chemical binding of Ni nanoparticles significantly reduce activity changes during the first hours on stream. Overall, this study demonstrates that the support and the corresponding metal–support interactions not only affect reaction pathways and activity, but also the pretreatment and activation required to reach a stable operating point, which is of crucial importance in kinetic catalysis research. Full article

Ammonia (NH₃) is a compelling carbon-free hydrogen carrier. Its catalytic decomposition to produce a hydrogen/nitrogen (H₂/N₂) gas stream is central to the “NH₃-H₂” clean energy cycle, provided that residual NH₃ is removed to fuel-cell-grade purity downstream. This review integrates advances from the past five years across four major catalytic NH₃ decomposition pathways, encompassing conventional thermocatalysis, plasma-catalytic, photo(thermal), and electrically driven catalysis, within a unified mechanistic and practical framework, distinguishing it from existing single-pathway reviews. Noble metal catalysts, particularly Ru-based systems, achieve superior low-temperature activity through support engineering, promoter effects, and active-site construction. However, our analysis reveals that non-noble metal (Fe, Co, Ni) catalysts and their alloys, nitrides, and carbides have made substantial progress, with certain Co-based and bimetallic systems approaching Ru-level performance via interfacial oxygen vacancy engineering and electronic structure modulation. Emerging non-thermal routes effectively overcome thermodynamic barriers, enabling operation at temperatures 200–300 °C below conventional thermal requirements, though each faces distinct challenges in energy efficiency, stability, and scalability. Key challenges remaining across all pathways to practical implementation, including residual NH₃ removal and H₂ purification, catalyst deactivation and stability, heat management and energy efficiency, start-up/shut-down dynamics, as well as system integration and economics, are critically assessed. This review provides theoretical guidance and practical recommendations for developing scalable, low-temperature NH₃ decomposition technologies. Full article

Carbon dioxide (CO₂) conversion in non-thermal plasma is a promising route for carbon utilisation under mild conditions. This study investigates the performance and dynamic behaviour of kaolin-based catalysts modified with Ni (nickel), Ni–Ce (nickel-cerium), and Fe–Cu (iron-copper) oxides in a Dielectric Barrier Discharge (DBD) reactor. Materials were characterised using X-ray diffraction, energy-dispersive X-ray fluorescence, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. CO₂ conversion was evaluated at varying Plasma Energy Numbers (PEN = 1.65–20) with time-resolved gas analysis over a 10 min period. Results demonstrate that the kaolin support is not inert; its dielectric properties actively influence discharge characteristics. Ni-based catalysts exhibited the highest stable activity, reaching ~53% conversion for samples calcined at 500 °C. Conversely, adding cerium oxide significantly decreased conversion and induced temporal instabilities, contrasting with its typical role in thermal catalysis. Time-resolved measurements revealed that Ni–Ce and Fe–Cu systems exhibit initial activity followed by gradual deactivation, suggesting plasma-induced surface restructuring. These findings highlight that catalyst performance in DBD is governed by a complex interplay of chemical activity and plasma–material interactions. The generated time-series data provide a robust foundation for machine learning applications in predictive modelling and stability classification of plasma-catalytic systems. Full article

Biomass valorization plays a vital role in achieving carbon neutrality and circular economy frameworks. Owing to its carbon-rich structure, biomass represents a promising feedstock to produce bio-based hydrocarbons via biological and thermochemical pathways. While biological conversion routes have been extensively studied, their deployment at commercial scale is constrained by high capital costs and low product yields. In contrast, thermochemical conversion technologies are increasingly being explored as viable large-scale biomass valorization routes. This review presents a comprehensive assessment of thermochemical pathways, with particular emphasis on hydrothermal liquefaction (HTL). The review identifies hydrothermal liquefaction (HTL) as a strategically advantageous route for wet and heterogeneous biomass valorization, due to simultaneous yields of liquid biocrude, and solid hydrochar. The review emphasizes the application of biocrude upgradation processes like hydrodeoxygenation under biphasic solvent systems using sulfided NiMo and CoMo catalysts. Further, the review also establishes hydrochar as a tunable functional material rather than a mere byproduct for applications in fields of energy production, soil amendment, and heterogeneous catalysis. The review article examines technology readiness levels of different biomass valorization techniques, and suggests that while combustion, anaerobic digestion, torrefaction, and transesterification are commercially mature, HTL and carbon capture utilization and storage (CCUS)-integrated fuel synthesis pathways remain at intermediate readiness. Additionally, the review carries out an in-depth study on artificial intelligence and machine learning (AI and ML) applications in biomass valorization, where it observes that Tree-based ensemble models, particularly Random Forest and XGBoost, show strong performance for several HTL prediction tasks, while Gaussian Process Regression and neural network–Bayesian optimization approaches provide additional advantages for uncertainty estimation and process-level optimization. Finally, the future research opportunities in biomass valorization and AI/ML application in HTL-process optimization have been identified for improving the bio-based fuel production techniques. Full article

Plant growth-promoting rhizobacteria (PGPR) foster sustainable and environmentally friendly agriculture by promoting plant growth and development. PGPR colonize the root rhizosphere, rhizoplane and root tissues, where they drive organic matter turnover and nutrient cycling, thereby increasing the (phyto)availability of essential macro- (P, N, K, S, Ca, Mg) and micronutrients (Fe, Zn, Mn, Mo, Co, Ni, Cu, B). This process relies on various mechanisms, including acid secretion (rhizospheric acidification and metal chelation), siderophore production (binding Fe, Zn, and other metals) and hydrolytic enzyme-mediated catalysis (phosphatases, phytases). Some of these microorganisms can also modulate the phytohormonal balance, reshaping root architecture and enhancing nutrient uptake, and even can alleviate abiotic stress or serve as biocontrol agents, contributing to pathogen resistance. Even though plant cultivation practices relying solely on synthetic fertilizers rapidly increase crop yield and productivity, they eventually result in crops poor in essential micronutrients and trace elements. This may contribute to micronutrient malnutrition in the human population. On the contrary, PGPR enhance both crop yield and nutritional quality. Therefore, in utilization with other nutrient sources, PGPR provide a promising and scalable approach towards advancing environmentally sustainable agriculture systems. Full article

Plasma-catalytic oxidation is a promising approach for the abatement of volatile organic compounds (VOCs), yet its efficiency is often limited by the ineffective utilization of plasma-generated reactive oxygen species and incomplete oxidation pathways. In this work, a composite catalyst was constructed by integrating spinel-type NiCo₂O₄ with three-dimensional cubic mesoporous KIT-6 to couple efficient mass transfer with redox-active surface functionality for plasma-catalytic degradation of toluene. The performance of NiCo/KIT-6 was systematically evaluated in a dielectric barrier discharge (DBD) reactor and compared with Ni/KIT-6, Co/KIT-6, and NTP-only systems. XPS, O₂-TPD, H₂-TPR, and apparent dielectric measurements were employed to elucidate catalyst properties relevant to plasma–surface interactions. NiCo/KIT-6 exhibits superior overall performance in terms of toluene conversion, CO_x selectivity, and CO₂ selectivity over a wide range of specific input energies. This enhancement is closely associated with the integrated regulation of surface redox properties, oxygen activation capability, and apparent dielectric response by the NiCo₂O₄/KIT-6 composite structure, which may promote reactive oxygen utilization and facilitates effective plasma–surface redox processes. These results provide insights into the rational design of composite catalysts for plasma-assisted oxidation of aromatic VOCs. Full article

The incorporation of polar functional groups into polyethylene (PE) chains at controlled concentrations enables tailored multi-functionality, manifesting as printability enhancement, improved dyeability, and enhanced blending compatibility with diverse polymeric materials. The most effective way to incorporate polar monomers into the PE macromolecules is the transition metal-mediated coordination–insertion copolymerization of ethylene with polar monomers. However, the Lewis basic heteroatoms (N, O, S, P, etc.) in polar monomers are prone to strongly coordinate to the catalytic center, resulting in irreversible catalyst deactivation. Owing to the nature of tolerance to Lewis basic functionalities, rationally designed Pd and Ni complexes have proven to catalyze direct coordination polymerization of ethylene with polar monomers, which opened a practical way to prepare functionalized polyethylenes (F-PEs). In this context, we summarize the recent advances of the Pd and Ni complexes catalyzed copolymerization of ethylene with various polar monomers, especially focused on those commercial polar monomer feedstocks. In addition, the effects of metal, ligand structural modification, and additives regulation on the catalytic performances were analyzed in detail. Some key ideas on the salient aspects of the catalyst are presented, and the challenges and prospects of Pd and Ni catalysts in the polar monomer copolymerization problems are also discussed. Full article

This work presents a comprehensive investigation of the thermal decomposition of nickel oxalate dihydrate as a precursor for the synthesis of porous NiO, with particular emphasis on microstructural formation and evolution. The transformations occurring at successive stages of the reaction were examined using SEM, TEM, N₂ adsorption, TG–DSC–MS, and in situ powder XRD, enabling the mechanisms of pore formation to be elucidated. The decomposition results in the formation of a porous pseudomorph composed of NiO nanoparticles with an average size of approximately 4 nm. This is the first time that the resulting microstructure has been shown to exhibit hierarchical, bimodal porous architecture. During dehydration, macropores are generated as a result of crystal fragmentation into blocks several hundred nanometers in size. Subsequent oxalate decomposition leads to the formation of mesoporous aggregates composed of nanometer-sized particles. The factors governing the parameters of the porous microstructure are analyzed. The resulting NiO, with its hierarchical pore structure, shows significant potential for applications in heterogeneous catalysis, gas sensing, and as electrodes for supercapacitors, lithium-ion batteries, and photoelectrochemical devices, as its macropores facilitate mass transport by reducing diffusion resistance while its mesopores provide a large accessible surface area for adsorption and catalytic reactions. Full article

High-entropy oxide (HEO) thin films hold significant potential for applications in spintronics and catalysis; however, their widespread utilization is hindered by weak room-temperature ferromagnetism (RTFM). Herein, we demonstrate a facile vacuum annealing strategy to enhance the RTFM of HEO thin films. (FeNiAlCrMn)O films exhibit a saturation magnetization (M_S) of 5.9 emu/cm³ and a Curie temperature (T_C) of 350 K after vacuum annealing at 1173 K. Mechanistic investigations reveal that the enhanced RTFM originates from an annealing-induced phase transition from rocksalt-to-spinel. Structurally, annealing facilitates cation diffusion from octahedral to tetrahedral sites, forming a highly crystalline, long-range magnetic lattice of spinel ferrite. Electronically, tetrahedral occupation shortens M–O bonds, drives electron transfer toward metal cations, and enhances orbital hybridization, thereby strengthening magnetic exchange coupling. This study provides a simple and effective strategy for tailoring the RTFM of HEO thin films. Full article

The efficient removal of low-concentration antibiotics from wastewater is a persistent challenge. In this work, we enhance the performance of a W-BiVO₄ photoanode by modifying it with CoNi-based metal–organic framework nanosheets (CoNi-MOF), constructing a W-BiVO₄@CoNi-MOFN composite. This integration markedly improves the separation and migration of photogenerated charge carriers. Consequently, the modified photoanode delivers a substantially higher photocurrent density of 3.92 mA cm⁻² at 1.23 V_RHE, representing a 2.3-fold enhancement over the pristine W-BiVO₄ (1.74 mA cm⁻²). Furthermore, the photoelectrocatalytic (PEC) system employing the W-BiVO₄@CoNi-MOFN photoanode demonstrates significantly superior degradation efficiency for low-concentration tetracycline compared to the system based on unmodified W-BiVO₄. The performance enhancement is attributed to a dual mechanism. First, the CoNi-MOF modification optimizes the PEC performance of W-BiVO₄, facilitating the generation of photogenerated holes and active oxidants. Second, the composite photoanode exhibits enhanced tetracycline adsorption via π–π stacking and hydrogen bonding, thereby promoting degradation kinetics. The photoanode also shows excellent reusability. Total organic carbon (TOC) analysis and biotoxicity tests confirm effective mineralization and reduced environmental toxicity. Furthermore, the system demonstrates promising concurrent cathodic hydrogen evolution. This work highlights the potential of the W-BiVO₄@CoNi-MOFN-based PEC system for integrated wastewater treatment and hydrogen production. Full article

Chelating agents can extend the operational pH range of iron-based advanced oxidation processes, yet comprehensive studies on chelated Fe-activated persulfate systems for textile dye degradation remain scarce. This study establishes an integrated framework for optimizing Fe(II)/persulfate (PS) systems using chelating ligands and hybrid energy inputs under near-neutral conditions. Among the tested systems, Fe(II)/PS complexed with citric acid (CA) exhibited superior performance, achieving ~91% dye removal within 20 min at pH 6.5 under optimized conditions (1.25 mM Fe(II), 10 mM PS, 0.1 mM CA). Chelation stabilized Fe redox cycling and prevented precipitation, enabling effective catalysis across pH 3–10. Optimal CA/Fe and Fe/PS ratios (0.1:1.25 and 1.25:10) yielded ~96% decolorization and 67.65% TOC removal in 60 min, while excessive chelation reduced activity. Transition metal screening (Mn(II), Zn(II), Cu(II), Co(II), and Ni(II) confirmed Fe(II) as the most effective activator, providing removal efficiencies up to 3.2-fold higher than competing metals. Mixed-dye experiments showed competitive degradation, with >37% color removal after 60 min for ternary dye mixtures. Mineralization reached ~92% TOC reduction after 120 min, indicating deep oxidation beyond chromophore cleavage. Reactive species quenching revealed a mixed oxidation mechanism involving ^•OH radicals and high-valent Fe(IV) species. Hybrid assistance improved mineralization, with UVC increasing TOC removal by 15.6%, while solar irradiation provided moderate enhancement under low-energy input. In contrast, low-power ultrasound (40 kHz, 60 W) delivered only 17.6 W acoustic power to the solution and did not improve performance due to limited cavitation and mixing. This work thus contributes a robust platform for advancing chelated iron-persulfate oxidation systems toward practical, effective treatment of recalcitrant dye-contaminated wastewaters under near-neutral conditions. Full article

N,N-Dimethyl-1,3-propanediamine (DMAPA) is an important aliphatic diamine widely used in fine chemical manufacturing. Its industrial production traditionally relies on Raney nickel catalysts, which suffer from pyrophoric hazards and limited selectivity due to imine condensation side reactions. To address these challenges, we report an Al₂O₃-supported Ni-Cu alloy catalyst as an efficient alternative for the selective hydrogenation of N,N-dimethylaminopropionitrile (DMAPN). The optimized Ni₃₀Cu₅/Al₂O₃ catalyst achieves complete DMAPN conversion and over 90% DMAPA selectivity under industrially relevant conditions (120 °C, 2.5 MPa H₂). X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy analyses confirm the formation of substitutional Ni-Cu alloy nanoparticles, where Cu incorporation induces both geometric isolation of Ni ensembles and electronic modulation of surface active sites, thereby suppressing condensation-derived by-products. In addition, an NH₃/ethanol-assisted process further improves selectivity while reducing autogenous operating pressure. Overall, this work demonstrates a safe and highly selective catalytic system for primary diamine synthesis, providing a practical alternative to conventional Raney Ni-based processes. Full article